We have studied 44 GA patients on the PCRU, have identified 40 OAT mutations in patients with GA including 26 alleles. Most recently we have produced a mouse model for OAT deficiency by targeted disruption & are beginning experiments in this model which are preliminary to anticipated gene therapy trials in GA. In brief,our data suggest that chronic reduction of ornithine slows or may even stop the progression of the chorioretinal degeneration.Unfortunately, only about 20% of patients are able to follow the highly restrictive diet.